code: def download_model(url):
      """Downloads a model file and puts it under model directory.
  
      It downloads a file from the URL and puts it under model directory.
      For exmaple, if :obj:`url` is `http://example.com/subdir/model.npz`,
      the pretrained weights file will be saved to
      `$CHAINER_DATASET_ROOT/pfnet/chainercv/models/model.npz`.
      If there is already a file at the destination path,
      it just returns the path without downloading the same file.
  
      Args:
          url (string): URL to download from.
  
      Returns:
          string: Path to the downloaded file.
  
      """
      # To support ChainerMN, the target directory should be locked.
      with filelock.FileLock(
          os.path.join(
              get_dataset_directory(
                  os.path.join("pfnet", "chainercv", ".lock")
              ),
              "models.lock",
          )
      ):
          root = get_dataset_directory(
              os.path.join("pfnet", "chainercv", "models")
          )
          basename = os.path.basename(url)
          path = os.path.join(root, basename)
          if not os.path.exists(path):
              cache_path = cached_download(url)
              os.rename(cache_path, path)
          return path
  
file_path: chainercv/chainercv/utils/download.py
imports: from __future__ import division
  from __future__ import print_function
  from distutils.util import strtobool
  import hashlib
  import os
  import shutil
  import tarfile
  import tempfile
  import zipfile
  import filelock
  from six.moves.urllib import request
  import sys
  import time
  from chainer.dataset.download import get_dataset_directory
  from chainer.dataset.download import get_dataset_root
label_desc: Use image node_id 3 for calling a global function with example usage: download_model(url) and returns: path